1. Field of the Invention
This invention relates to a semiconductor device, and particularly to a conductor film and fabricating method therefor applied suitably to large scale integration (LSI) circuit devices.
2. Description of the Prior Art
Among the known conductor film materials used for integrated circuit devices are aluminum to which is added a small quantity of copper, and aluminum to which is added a small quantity of silicon or precious metal. The conductor film of aluminum to which is added a small quantity of copper is described in U.S. Pat. No. 3,725,309 as being excellent in resistivity against electromigration, i.e. in the effectiveness of preventing the breakage of conductor film attributable to electromigration.
The conductor of a semiconductor device is generally made of aluminum to which is added several percent of silicon. When the device is operated to conduct a large current at a high temperature, the current flowing in the aluminum conductor film causes atoms of the film to move, resulting in the formation of hillocks in one section and voids in another section of the conductor film. A grown hillcock causes a short-circuit between interconnecting conductors, while a grown void causes an increased resistance of conductor at the portion of void and eventually a failure of conductor by heat generation, and both cases result in a malfunctioning of the semiconductor device.
In order to overcome the problem of electromigration, according to the above U.S. Patent, 0.1-54 weight-% of copper is added to aluminum so that a precipitation structure of CuAl.sub.2 particles is formed. The particles precipitate at grain boundaries and grain boundary triple points of the aluminum matrix to prevent the movement of aluminum atoms, and consequently the semiconductor device can have an extended life against electromigration. However, CuAl.sub.2 is highly apt to segregate, and the semiconductor device suffers a premature failure due to electromigration at portions where CuAl.sub.2 is not precipitated.
Al--Cu alloy exhibits difficulty in fine pattern formation using dry etching, and is corroded severely by
Cl and residual Cl.sup.31 ion during processing, and therefore it is extremely difficult to have a forming accuracy of 1 .mu.m or submicron pattern. Another problem in the operation of the semiconductor device is the reliability under humid conditions.
The Al conductor film is coated with a passivation film for surface protection, which exerts a tensional stress on the conductor film until it is broken, and this defect caused by so-called stress migration is also a problem. Specifically, the Al--Cu conductor, which has a poor pattern accuracy, is prone to break at a narrow portion.
Japanese Patent Unexamined Publication JP-A-60-26640 discloses conductor materials consisting of aluminum, precious metals (Pt, Pd, Rh, Ir) and silicon, and another Japanese Patent Unexamined Publication JP-A-61-144847 discloses a semiconductor device having a conductor film formed of alloy including at least one of Pd and Pt by 0.1-2 weight-% and precipitated in the form of metal or compound. These wiring film materials are deposited on a semiconductor substrate by evaporative deposition or sputtering, and then formed into an intended pattern mainly by the wet-etching process.
In the conventional technique, where the Al conductor film has an enhanced electromigration resistance by the addition of Cu to Al, the segregation of Cu is yet unconsidered, resulting in a significant variability of life time among production lots. Since Al--Cu alloy is less resistive against corrosion, it is unfavorable for fine pattern formation by dry etching or wet etching, and also suffers a so-called migration problem in which the film is broken at a defective portion created in the etching process under the stress caused by the passivation film.
The materials and devices in the above-mentioned Japanese Patent Unexamined Publication JP-A-60-26640 and No. 61-144847 are also in need of improvement of resistances against electromigration and stress migration.
The foregoing conventional techniques do not consider patterning of the conductor film materials by dry etching and problems encountered in the process. The Japanese Patent Unexamined Publication JP-A-61-144847 mentions dry etching, but discloses nothing about associated problems.
The inventors of the present invention has found the fact that when an aluminum conductor film or aluminum-based alloy conductor film including a small quantity of precious metal, silicon, copper, etc. added to aluminum is subjected to dry etching, the conductor film has its side wall etched slantwise (will be termed "side etching"), creating a difference in the pattern profile between the top and bottom line width. Although wet etching is free from the side etching problem, it is merely capable of forming lines down to several .mu.m at most and is not suited for fine pattern formation of 1 .mu.m or smaller.
With the intention of further increasing the integration density of LSI devices, the line width of conductor film has come to be narrower, and the etching technique capable of pattern formation with a line width of 1.3 .mu.m or less would be increasingly important.